Recent years have seen unprecedented dramatic changes in the communication transmission field due to continuous and rapid development of electronic and material technologies. The two major trends of such changes are: the gradual replacement of the traditional wired transmission systems by their wireless counterparts, whose transmission medium is the air; and the gradual replacement of the traditional metallic-medium-based telecommunications systems by their fiber-optic counterparts, which transmit optical signals through optical fibers.
Take the fiber-optic telecommunication systems for example. Thanks to the development of fiber-optic materials, fiber-optic telecommunication has reached maturity in both theory and application since the 1960s. Optical fibers feature a small diameter, light weight, ample sources of materials, and a strength comparable to that of copper wires. Therefore, when used in data transfer, optical fibers have such advantages as large bandwidths, low losses, and high resistance to electromagnetic interference. As people demand larger and larger amounts of data be transferred at increasingly higher transfer rates, optical fibers undoubtedly provide the best solution to innovation of the existing communication systems. In a fiber-optic communication system, fiber-optic transceivers are critical components on which the quality of optical signal transmission depends. As shown in FIG. 1, the fiber-optic transceiver 100 is connected to an electronic device (not shown) and is controlled thereby to generate or receive a laser beam. The fiber-optic transceiver 100 essentially includes a controller IC 101, a laser driver 102, a transmitter optical subassembly (TOSA) 103, a post-amplifier 104, a receiver optical subassembly (ROSA) 105, and a thermal sensor 106. The TOSA 103 is provided therein with a laser diode 1031, a monitoring photodiode 1032, and a post-system-on-chip controller (post-SoC controller) 1033. The ROSA 105 is provided therein with a photo-detector 1051 and a pre-amplifier 1052. The laser driver 102 is configured for providing, under control of the controller IC 101, a direct-current (DC) bias current to the laser diode 1031, thereby driving the laser diode 1031 to generate a laser beam, which is transmitted outward through an optical fiber 201. The photo-detector 1051 is configured for measuring the laser beam transmitted from another optical fiber 202, and this laser beam is sequentially amplified by the pre-amplifier 1052 and the post-amplifier 104 before it is delivered to the controller IC 101. The thermal sensor 106 serves to measure the working temperature of the laser diode 1031. The monitoring photodiode 1032 and the post-SoC controller 1033, on the other hand, serve to monitor the laser beam generated by the laser diode 1031.
Conventionally, referring again to FIG. 1, the controller IC 101 corrects its control signal to the laser driver 102 according to the working temperature of the laser diode 1031 measured by the thermal sensor 106. Thus, temperature compensation is performed on the bias current or modulation current generated by the laser driver 102, allowing the laser beam generated by the laser diode 1031 to have the optimal optical power and extinction ratio (ER) in different temperature ranges. Some fiber-optic transceivers are so designed that the thermal sensor 106 is directly provided in the laser driver 102 or the TOSA 103. The controller IC 101 also determines whether the laser beam monitored by the monitoring photodiode 1032 is normal in terms of brightness and stability. Then, the controller IC 101 adjusts its control signal to the laser driver 102 accordingly to correct the current generated by the laser driver 102, with a view to keeping the current in a correctly stable state.
As abnormality in laser beam brightness or stability results mainly from a high or low working temperature of the laser diode 1031, one effective approach to increasing the performance and service life of the fiber-optic transceiver 100 is to make a lookup table of the operation parameters of the laser diode 1031 at different working temperatures. Once the lookup table is available, the controller IC 101 can search the lookup table for the operation parameters corresponding to the current temperature of the laser diode 1031 and adjust the control signal according to the operation parameters. This ensures that the current generated by the laser driver 102 will cause the laser diode 1031 to emit a laser beam having the optimal optical power and extinction ratio regardless of the working temperature of the laser diode 1031. In other words, temperature compensation will be effectively carried out to greatly enhance laser beam stability.
According to the above, in order for the fiber-optic transceiver 100 to control the laser driver 102 in such a way that the optical power and extinction ratio of the laser beam generated by the laser diode 1031 stay at the optimal levels throughout an entire temperature range, either of the following two schemes can be used:
(1) The controller IC 101 uses the monitoring photodiode 1032 in conjunction with a closed-loop control circuit (not shown) to monitor the laser beam generated by the laser diode 1031. Then, the controller IC 101 controls the laser driver 102 according to the monitoring result so that the optical power and extinction ratio of the laser beam generated by the laser diode 1031 remain at the optimal levels.
(2) The controller IC 101 measures the current working temperature of the laser diode 1031 with the thermal sensor 106, checks a pre-set lookup table in the controller IC 101 for the operation parameters corresponding to the current working temperature of the laser diode 1031, and controls the laser driver 102 according to the operation parameters so that the optical power and extinction ratio of the laser beam generated by the laser diode 1031 stay optimal.
However, no matter which of the foregoing schemes is used, the fiber-optic transceiver 100 cannot control the optical power and extinction ratio of a laser beam over an entire temperature range unless: (1) the TOSA 103 is provided therein with the monitoring photodiode 1032 and the post-SoC controller 1033 for monitoring the laser beam generated by the laser diode 1031, and (2) the closed-loop control circuit is precisely designed and is configured for fast response; or unless repeated tests have been conducted on the laser diode 1031 to obtain a large amount of data that correspond to the operation parameters in the entire temperature range. All of the above not only adds to the complexity and cost of the fiber-optic transceiver 100 in both design and manufacture, but also causes a lot of trouble to companies with limited chip design capabilities.
Therefore, the issue to be addressed by the present invention is to make commercially available fiber-optic transceivers easily applicable to a fiber-optic communication system and to enable the fiber-optic transceivers in a fiber-optic communication system to control the optical power and extinction ratio of a laser beam automatically, rapidly, and cost-effectively in the absence of the monitoring photodiode 1032, the aforesaid lookup table, and the aforesaid closed-loop control circuit, thereby keeping the optical power and extinction ratio of the laser beam at the expected optimal levels over an entire temperature range.